MM-28859 Add feature flag managment system using split.io and remove viper. (#15954)

* Add feature flag managment system using split.io and remove viper.

* Fixing tests.

* Attempt to fix postgres tests.

* Fix watch filepath for advanced logging.

* Review fixes.

* Some error wrapping.

* Remove unessisary store interface.

* Desanitize SplitKey

* Simplify.

* Review feedback.

* Rename split mlog adatper to split logger.

* fsInner

* Style.

* Restore oldcfg test.

* Downgrading non-actionable feature flag errors to warnings.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

vendor/github.com/splitio/go-split-commons/v2/push/split.go

@@ -0,0 +1,77 @@
+package push
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"sync/atomic"
+
+	"github.com/splitio/go-split-commons/v2/dtos"
+	"github.com/splitio/go-toolkit/v3/logging"
+)
+
+// SplitUpdateWorker struct
+type SplitUpdateWorker struct {
+	activeGoroutines *sync.WaitGroup
+	splitQueue       chan dtos.SplitChangeNotification
+	handler          func(till *int64) error
+	logger           logging.LoggerInterface
+	stop             chan struct{}
+	running          atomic.Value
+}
+
+// NewSplitUpdateWorker creates SplitUpdateWorker
+func NewSplitUpdateWorker(splitQueue chan dtos.SplitChangeNotification, handler func(till *int64) error, logger logging.LoggerInterface) (*SplitUpdateWorker, error) {
+	if cap(splitQueue) < 5000 {
+		return nil, errors.New("")
+	}
+	running := atomic.Value{}
+	running.Store(false)
+
+	return &SplitUpdateWorker{
+		activeGoroutines: &sync.WaitGroup{},
+		splitQueue:       splitQueue,
+		handler:          handler,
+		logger:           logger,
+		running:          running,
+		stop:             make(chan struct{}, 1),
+	}, nil
+}
+
+// Start starts worker
+func (s *SplitUpdateWorker) Start() {
+	s.logger.Debug("Started SplitUpdateWorker")
+	if s.IsRunning() {
+		s.logger.Info("Split worker is already running")
+		return
+	}
+	s.running.Store(true)
+	go func() {
+		for {
+			select {
+			case splitUpdate := <-s.splitQueue:
+				s.logger.Debug("Received Split update and proceding to perform fetch")
+				s.logger.Debug(fmt.Sprintf("ChangeNumber: %d", splitUpdate.ChangeNumber))
+				err := s.handler(&splitUpdate.ChangeNumber)
+				if err != nil {
+					s.logger.Error(err)
+				}
+			case <-s.stop:
+				return
+			}
+		}
+	}()
+}
+
+// Stop stops worker
+func (s *SplitUpdateWorker) Stop() {
+	if s.IsRunning() {
+		s.stop <- struct{}{}
+		s.running.Store(false)
+	}
+}
+
+// IsRunning indicates if worker is running or not
+func (s *SplitUpdateWorker) IsRunning() bool {
+	return s.running.Load().(bool)
+}